Description of the Related Art
It is known to manufacture electrical solders for connecting an electronic component to a wiring circuit. Generally, solders are alloys of elemental metals that are formed into a paste or wire. The solder paste or wire is heated to melt to form a solder joint between the electronic components and circuits.
High speed electronic manufacturing generally utilizes printed solder pastes. The solders are placed atop strategic areas of an electronic circuit. Electronic components are placed atop the solder paste and the assembly is heated in an oven until the solder paste melts and bonds the electronic component to the circuit. A wide variety of solder compositions exist to secure electronic components to the circuits. Recently, environmental regulations have spurred the development of lead free-solder alloys which are preferred over solders that contain lead. Additionally, the develpoment of low temperature substrates is driving the use of lower temperature soldering processes.
The disadvantage of using solder paste or solder wire is that the temperature required to melt the solder and cause it to flow damages fragile electronic components or delicate substrates used for wiring circuit substrates. Generally, even low temperature solders melt between 110 to 165.degree. C. This requires that substrate material and electronic components be made from material that can withstand a prolonged exposure to these temperatures. It is desirable to manufacture substrates and components from materials that are generally damaged by temperature in excess of 100-150.degree. C. While the compositions and methods of the present invention are suitable for all types of substrates and higher temperature soldering, they are especially useful for lower temperature applications. It is desirable to use polymeric substrates of low cost and light weight materials such as Acrylonitrira Butadiene Styrene (ABS), Polyethylene Terephthalate (PET) and Potyamide (nylon--PA). These low cost, light weight substrates may become damaged when heated above 105.degree. C. A composition that may be soldered at lower temperatures allows these materials to be used as substrates.
It is also desirable to manufacture substrates having a three dimensional contour. Circuits made with a three dimensional contour allow for greater flexibility when manufacturing and designing electronic components. Components may be attached on horizontal, semi-horizontal; curved or vertical surfaces of the circuit. The housing of the electronic device may serve a dual function and act as both a substrate for an electronic circuit as well as the housing for the electronic device. One automotive application that uses this technique is surface mounting electronic components directly atop automotive components. It is desirable to use three dimensional surfaces, such as ventilating ducts, as the substrate for electronic circuits as illustrated in commonly assigned U.S. patent application 08/642,287.
Heretofore, it has been difficult to manufacture electronic components and modules that have a highly contoured three dimensional surface because conventional high speed solder paste equipment relies on transfer platens or stencils to transfer the solder paste to the substrate. These stencils or platens work best with flat, two dimensional surfaces. Neither the stencils nor the platens work on the three dimensional surfaces.
In another aspect of the present invention, it is generally known that the surface properties of a material may be enhanced or modified with the application of a thermal spray. Thermal spray coatings include carbides, ceramics, metallics, cermets and plastics. Thermal spray coatings are commonly used to resist erosion, abrasion or to protect the underlying components from excessive temperature, oxidation or wear. Heretofore, thermal sprays have not been used to provide the basis for an electronic interconnect between an electronic component and a circuit.